Power system



POWER SYSTEM D. w. MGQLENEGAN Original Filed Dec. 29, 1937 InventorDavid W. McLenegan, b film 8 Hi May 9, 1939.

SE mm mm Emma mm mm Attorney.

Patented May 9, 1939 rice PATET POWER SYSTEM David W. McLenegan,Caldwell, N. J., asslgnor to General Electric Company, a corporation ofNew York Application December 29, 1937 Serial No. 182,275

Renewed January 26, 1939 4 Claims.

My invention relates to alternating current power systems havingvariable speed prime movers or other power devices and particularly tosuch systems for supplying power to drive auxiliary apparatus on railwaycars or other vehicles.

Air conditioningsystems and other auxiliary apparatus utilized onrailway cars are commonly provided with power supplied from a suitableelectric generator driven by one of the car axles. For most purposes, itis satisfactory to use a direct current generator. However, when airconditioning systems are provided with hermetically sealed compressorunits; that is, units in which the motor and compressor are contained ina sealed casing, an induction motor should be used and it necessary toprovide a source of alternating current. The speed of an alternatingcurrent motor is, dependent upon the irequency of the current suppliedand this in turn is determined by the speed of the generator. In orderto utilize alternating current supplied from a generator driven by thecar axle, it is necessary to provide some arrangement for keeping therange of frequency of the generated current su cientiy narrow forsatisfactory operation of the motors. This is particularly true when themotors are employed to drive apparatus such as refrigerant compressors,the reirigeratin capac= ity of which varies with the speed. Accordingly,it is an object of my invention to provide an in proved alternatingcurrent power system having a variable speed prime mover such as theaxle of a railway vehicle and including an arrangewent whereby the speedof the motors to which the power is sup lied he maintained within a.range substantially narrower than the range of speed oi the prime mover.

Further objects and advantages of my haven- 49 tion will become apparentastlie following description proceeds, and the features of novelty whichcharacterize my invention will be pointed out particularity in theclaims annexed to and forming a part oi this specification.

For a better understanding of my invention,

reierence may be had to the accompanying drawing in which Fig. 1 shows apassenger railway car provided with an electrically driven airconditioning system and an alternating current 5 power system embodyingmy invention for supplying energy to the air conditioning apparatus;

and Fig. 2 is a wiring diagram of the power system utilized on the carshown in Fig. l.

Referring now to the drawing, I have shown railway car provided with a.refrigerant condensing unit it! including a hermetically sealed casing II in which is arranged a refrigerant compressor driven by an alternatingcurrent induction motor. The condensing unit In also includes condensersl2 and a fanl3 driven by analternating current motor it for circulatingair over the casing H and over the condensers. The condensing unit isarranged to supply liquid refrigerant to the cooling coils of an airconditioning system including a cooling chamber it within which theevaporator 10 coils are arranged and a motor it for driving a fan todistribute the cooled air from a conduit it through openings it into theupper portion of the passenger space oi? the car. In order to supplyalternating current for energizing the compressor 16 motor and the motori l, I provide an alternating current generator ill driven by a belt Wfrom one of the car axles ii, a spring 22 being provided to maintaintension in the belt 2E2. Other forms of mechanical drive may he used fortransmitting g power from the car'axle to the generator, and any othersuitable variable speed power device may be used to drive the generatorit. in order to provide field excitation for the generator. it! and alsofor energizing the lighting system of the car and such apparatus as themotor it I provide a direct current generator of the type which isstandard on railway cars. The generator 23 is connected to be drivenfrom an axle 2 3 by a belt or any other suitable arrangement, a asspring is losing provided to maintain the belt tension. The alternatingcurrent genera-tor it) is arran ed, so that it may operate with a plurality of numbers of pairs of ileld poles in such manner that thefrequency oi the current pro- 35 duced thereby may he changed bychanging the number of poles; A dynamoelectrlc machine oil this type isdisclosed and claimed in U. 8. Letters Patent Llil loldpril 22, 1824-,Robert W. Wie5sman, assigned to the General Electric Goinpany, 4Qassignee of this invention. A frequency responsive device is providedfor changing the number of poles of the alternating current generatoriii in accordance with the speed oi the car, so that the frequency ofthe current produced by the 45 generator it] varies within a narrowerrange than the range of speeds-cf the car, and furthermore. thecompressor motor and the motor i i are designed to be operated at anyone of a plurality of speeds, the speeds being selected in mcordance sowith the frequency of the current produced by the generator i9, so thatthe speed of the motors varies within a narrower range than the range offrequency of the generated current. The variation in speed of thealternating current 55 field exciting winding 28.

, fore, four effective field poles.

motors is, therefore, much more narrow than the variationin speed of thegenerator l9, and the speed of the devices driven by the motors is,therefore, substantially uniform.

The arrangement and mode of operation oi the power system will readilybe understood by reference to Fig. 2, in which I have indicated at Hathe motor within the casing H shown in Fig. 1 to drive the compressor ofthe refrigerating machine. The motor Ha is provided with a low speedfield exciting winding 2'5 and a high speed The fan motor I4 is providedwith a low speed field exciting winding 29 and a high speed fieldexciting winding 30. The two windings are connected to be supplied inparallel, the low speed windings being connected to three-phase supplylines 3!, and the high speed windings to three-phase supply lines 32.Lines 3! and 32 are arranged to be connected by switches 33 and 3 3respectively, to three-phase alternating current supply lines 35, whichare connected to three terminals of a manually operable switch 36;Three-phase alternating current power is supplied to the switch 36either from three-phase lines 3'5 connected to the alternating currentgenerator 59 or from three-phase lines 38 connected to receive powerfrom a receptacle 39 when the train is in the station.

The generator 19 comprises a salient pole rotor having a plurality offield exciting windings 3d, which are connected so that opposite pairsor" windings are in series, the pairs shown on the vertical axis beingconnected to slip rings 4i and 42 at the right end of the rotor, and thepairs on the horizontal axis to slip rings 43'and 44 at the left end ofthe rotor. The field excitin winding has been illustrated with eightcoils providing a full number oi eight field poles. When the generatoris operating with its full number of poles, the magnetic flux inadjacent poles is in opposite directions as indicated by the arrows.erator with one-half its fullnumber oi poles, the current in the groupof coils connected in the left-hand rings 43 and 44 is reversed, itbeing evident that then the polarity of each oi the coils of thereversed group is the same as that of the adjacent coil of the othergroup. This connection provides four groups of coils, each groupcomprising two coils in which the direction of magnetic flux is the sameand there are, there- Each of the salient poles is provided with ashort-circulting ring or jacket 45 to damp-the flux changes produced bythe reversal of the fields when changing the number of poles of thegenerator. The stator of the generator 49' is provided with a pluralityof field exciting windings 4E and H arranged to provide either asingle-Y connection for the lower range of speeds, or adouble-Yconnection for the upper range of speeds. This change in the connectionof the stator windings compensates for the change of voltage due to thechange in speed. In order to change the number of pairs of poles on therotor of the generator 89, I provide solenoid operated switches 48 and49; and in order to change the connection of the windings of the stator,I provide solenoid operated switches 50 and 5|.

In the railway air conditioning system illustrated, the switches 50 and5| in addition to eifecting a change of the connection of the gen- Whenit is desired to operate the genof switch 48.

of switches is prevented by interlock contactors comprising the top armsof switches 48 and 49.

Operation of the pair of switches 48 and 5| con- 1 costs the generatoris with its full number of poles and with its stator winding insingle-Y. This is the connection for the lower range of train speeds.The pair of switches 49 and 50 connects the generator with one-half itsfull number of poles and with its stator winding in double-Y. This isthe connection for the upper range of train speeds. In addition to anelectrical interlock effective through the top arms of the switches 48and '49 to prevent concurrent actuation of the two pairs of switches, a.me-

. chanical interlock 53 is provided to prevent concurrent actuation ofthe switches 50 and 5|.

In order to actuate the pair of switches 48 and iii during the lowerrange of train speeds and the pair ofswitches 49 and 5|! during theupper range of speeds, I provide a switch 54 operated by relay contactor55 in accordance with the frequency of the voltage supplied by thegenerator to the lines 31. In its upper position, the switch 54 connectsthe solenoids o! the switches 48 and Si in parallel between lines 56 and51 through the top arm of switch 49, so that the switches 48 and 5! willbe actuated upon closing of the thermostat 52. The line 67 is connectedto one of the terminals of the direct current generator 28 and the line58 is connected to the other terminal through a. line 58a when thethermostat is operated. The pole changing operation can be e!- system isbeing supplied from the station source through the lines 38 does notoperate the pole In its lower position, the.

changing switches. switch 54 connects the coils of switches 49 and 50across the lines 55 and 51 through the top arm The switch 54 is actuatedby a relay employing a series non-linear resonant circuit including aresistance element 58, a saturable inductance element 59 and acapacitance element. arranged in series across lines 8|, which areconnected to be energized across one phase of the windings of thegenerator IS. A second capacitance element 62 is provided to change thecritical frequency for operatib'ri of the relay in such manner that therelay may eflect a change in the connections of the generator inaccordance with the speed of the train although the relay itself isresponsive to the frequency of the voltage'produced by the generator. Arelay. of this type is described and claimed in a copending application,Serial No. 182.268, filed De-,

cember 29, 1937, in the name of Chauncey G. Suits and assigned to thesame assignee as the present application. I do not, therefore, claimherein anything described or claimed in the said Suits application. Theoperation of the frequency responsive relay will be explained more fullyhereinafter.

Direct current is supplied by the generator B for energizing the cont?)1 circuits and the field of the alternating current generator l9 andany and 34 respectively. One of the coils 19 and auxiliary apparatus,such as the motor It and a plurality of lights 63. The generator 23 isof the type commonly employed on rail-lay cars, and is provided with ashunt field winding Gil and a field regulator 85. A. storage battery 86is provided to supply direct current when the train is not in motion.The battery is permanently connected across the supply line Etc and aline 6'6. A cutout 58 is provided to connect the battery to thegenerator for changing whenever the voltage of the generator is greaterthan that of the battery, this arrangement being standard for railwaylighting circuits. The lights 63 may be connected across the lines 56aand 61 by a switch 59, and the motor It may be connected across thelines 56a and 61 by a switch It in the event it is desired to run themotor continuously. A switch 10a is provided so that the circuit of themotor 16 may be opened to prevent automatic starting of the motor anddraining of the battery when the car is out of service.

When .the thermostat 52 calls for cooling, it moves to the left andconnects a coil "ll across the battery to actuate a switch 12, the coilit being across the battery through the line 55a and a line 13. Theupper contact of the switch 12 closes a holding circuit for the coil it.The

bottom contact connects the motor 86 across the battery, and anintermediate contact llconnects the field exciting winding of thegenerator i9 across the direct current generator 23 between the line 56aand a connection 16 through a line 16. The other intermediate contactindicated at 11 connects a line 18 to the line 56a to energize onesideof coils 19 and 8B of the switches 33 80 is energized by beingconnected between lines 13 and 18, the coil selected depending upon theposition of a switch 8!, and the corresponding one of the switches 33and 34 is, therefore, operated to connect either the high or low speedwindings of the motors Hit-and H to the supply V circuiting the batterywhen the coil is short-cirspeed, so that the frequency of the generatorI9 is halved and the generator supplies current at a frequency whichincreases with the increase of speed up to full car speed. It is readilyapparent that even with this reduction the range of the alternatingcurrent generator frequencies, there is still a wide variation offrequency and it is in order to reduce still further the range of motorspeeds that the alternating current motors are provided with the twospeed windings, as shown,

making it possible to operate the motors within a range of speed morenarrow than the range of frequency of the current supplied by thegenerator. In this manner, it is possible to operate the compressors orfans driven by the motors with relatively small speed variation.

In order to select the motor speeds and make the range of speeds of themotors more narrow than the range of frequency of the supplied current,I provide a relay it? for energizing a coil 83 to operate the switch 38.Any suitable fre quency responsive device or relay may be utilized tooperate the switch iii and select the one of the switches 33 and 3 3which is to be operated. I prefer, however, to employ relay utilizing aseries non-linear resonant circuit of the type disclosed and claimed inU. S. Letters Patent 2,021,753, Chauncey G. Suits on November 1935, andassigned to the Feneral Electric Company, assignee of this invention.The relay is connected to be responsive to the frequ icy of the voltageacross one phase of the lines and comprises a non-linear resonantcircuit including a saturable inductance element a resistance element85, and a capacitance element St connected in series between two of thelines The operating coil of the relay ti is connected across thecapacitance 86. A circuit of this type may be designed to have acharacteristic such that the voltage across the capacitance fallssuddenly at a critical value of frequency. On an increase of frequencyfrom minimum to maximum, the relay 82 will be picked up to energize thecoil 83 and pick up the switch ill thereby actuating the switch 34 andconnecting the high speed windings of the motors i la and Hi. When thecritical value of frequency is reached, the relay 82 will drop outthereby causing the switch hi to drop out and actuate the switch 33 toconnect the low speed windings of the motors to the lines 35. It will beevident that the operation of the motors with their high speed windingsat frequencies in the lower portion of the range of frequency willapproximate the speeds of operation of the mo-.

tors with the low speed windings at frequencies in higher portion of therange of frequencies. Any suitable arrangement for providing two speedranges for the motors may be employed. However. I prefer to use motorsprovided with two wi'ndingsas shown, the windings being arrangedtoprovide a difierent'number of effective poles. For example, in thesystem illustrated in which the generator is provided with anarrangement for halving the number of its field poles, I prefertoprovide motors having high and low speed windings giving a ratio ofspeeds of 3:2. For example, the motors might be provided with afour-pole high speed winding and a six-pole low speed winding.

In order to prevent excessive speed of the motors; for example, in theevent the train speed should become excessive, I provide a switch 81having an operating coil 88 arranged to be actuated by a relay 89 whenin its drop out position. The relay 89 is connected across a capacitance90 of a non-linear resonant circuit including a saturable inductanceelement 9! and a resistance element 82 connected in series with thecapacitance 90 across one phase of the supply lines 35. The non-linearresonance circuit is designed to pick up the relay 89 at all normalfrequencies of the voltage across the lines 35, so that the coil 88 isnormally deenergized. The critical frequency of the non-linear circuitis selected so that the relay drops out at a value of frequencycorresponding to the maximum frequency permissible for energlzatlon ofthe motors. When the relay 89 drops out the coil 88 of the switch 8!isenergized and the switch 81 is picked up j to open the circuits of thecoils l9 and 80 thereby preventing actuation of either of the switches33 and 34 so that the motors Na and M cannot be current supplied to themotors, I provide a reversing switch 93, which is arranged to reversetwo of the supply lines 35, and I provide a phase rotation responsivedevice M for actuating the switch 533. The device 9d comprises a smallpolyphase induction motor 95 having a relatively high resistancesquirrel cage rotor, or it may be any other suitable device havingsimilar characteristics. The three phase windings of the motor areconnected to the lines 35. When the phase rotation is in one directionthe motor 95 rotates in a clockwise direction and moves the switch 93 toits upper position through a train of gears 95 and a rack 9i. When thephase rotation is in the opposite direction, the motor turns in acounter-clockwise direction and moves the switch to the position shownin the drawing. It will, therefore be evident that the same direction ofphase rotation will be maintained in the lines 35 leading to the motorsregardless of the direction bf phase rotation at the terminals of theswitch 36.

scribed above, when the car leaves the station. manual switch 36is'closed in its lower position thereby connecting supply lines 35 tothe alternating current generator leads 3?. As soon as the car attainssufficient speed, the voltage of the direct current generator 23 willbuild up, and will rise toa value sufficient to close the cutout 58 andconnect the generator to charge the bat tery 68. Should there be ademand for cooling, the thermostat 52 will pick up the switch it and,since the switch 54 is in its drop out position, the coils of theswitches 49 and E] will be connected across the generator between thelines 55 and 5f and the switches 49 and 59 will be picked up. The

actuation of the switches 49 and 50 connects the generator with itsminimum number of poles, so that a relatively low frequency voltage isproduced. However, at the speed at which the direct current generator 23builds up, this frequency will be sufllcient to actuate the relay 55 andpick up switch rod indicated at Hli will continue to move upwardly ashort distance after the switch arm v This arrangehas engaged the uppercontacts. ment assures the maintaining of switch arm in engagement withthe upper contacts during the interval when the generator connectionsare being changed and, therefore, prevents the dropping out of theswitch due to the decrease of voltage during the interval of change. Thegenerator is now connected to supply the motor lines 35, and the relay32 will be picked up to actuate During the operation of the power systemdethe switch 8! and connect the coil 80 between the lines 18 and 13through an interlock arm I02 of switch 33. The switch 34 is, therefore,actuated to connect the high speed windings 28 and 30 of the motors tothe power supply. The motors Ila and I4 will then operate the condensingunit III to supply refrigerant to the coils within the cooling chamber55 and the cooled airwill be circulated by operation of the fan It anddelivered to the passenger compartment. As the train speed increases,the frequency of the current supplied by the generator will increaseuntil the critical frequency of the relay 82 is reached when the relaly82 will drop out deenergizing the coil 83 to cause the switch 8! to dropout and deenergize the coil Bil. When the coil 80 is deenergized, thehigh speed switch 34 opens. Switch 8! in its drop out position energizesthe coil 19 of the switch 39 through an interlock arm Hi3 of the switch3t and the switch 33 is, therefore, actuated to connect the low speedwindings of the motors to the supply lines 35. The increase in frequencyof the supplied current is, therefore, compensated by the reduction ofthe speed of the motors and the refrigerating apparatus is, therefore,driven at about the same range of speed as was effective with the highspeed windings during the lower range of frequency; As the generatorfrequency increases, it will increase to a value which is the criticalvalue for the resonant circuit of the relay 55 when only the condenser60 is connepted therein. Relay.55 will, therefore, drop out therebydeenergizing the switch 54 which drops out disconnecting the switches 48and 5| and energizing the switches 49 and 50. so that the generator isconnected with one-half its full number of poles and with its windingsin double- Y. When the switch 49 is picked up, the upper arm thereofconnects the capacitance 62 in parallel with the capacitance 60 of therelay 55 and thereby changes the characteristic of the nonlinearresonant circuit, so that the relay 55 will not be picked up until thefrequency is reduced and a frequency is reached less than one-half thecritical frequency of the circuit with only the.

capacitance 50. The reduction of the frequency due to the halving of thenumber of effective poles of the generator causes the relay 82 to bepicked up since the frequency has fallen below its critical drop outvalue and the motors are, therefore, connected so that their high speedwindings are energized by picking up of the switch 34. As the trainspeed continues to increase, the frequency of the current supplied bythe generator I9 will again reach the critical frequency of the relay 82and the relay will drop out to transfer the motors from their high speedto their low speed windings thereby lowering the speed of the motors andcompensating for the increase in frequency of the generator l9. Thesystem will continue to operate with the generator l9 connected with itsminimum number of poles and the motors connected with their low speedwindings until the train speed is again reduced or until the train speedbecomes excessive and causes operation of the over-frequency relay 89 todisconnect the motors from the lines 35. When the train speed isdecreased from the normal full speed, the mo-- tors and generator willbe connected in a sequence which is the reverse of .that just described.The motor windings will change from low to high speed when the frequencyof the generator decreases to the critical pick up frequency of therelay d2. When there is a further decrease of train speed, the criticalspeed for the relay 55 will arouses be reached and the relay 38 willpick up and energize the switch it which will change the generatorconnections from the lower number of poles to the full number of poles.This change will increase the frequency or the current supplied and therelay 32 will drop out thereby reconnecting the motors with their lowspeed winding energized. As the train speed is decreased still further,the critical pick up value of frequency tor the relay 82 will be reachedagain, the relay will pick up, energize the switch iii and transfer themotors from their low speed to their high speed connection. when thetrain speed is still further reduced, the voltage of the direct currentgenerator 23 will fall sufilciently to open the cutout B8 and deenergizethe control circuits thereby stopping operation oi the power system.

The previous description has been based on the assumption that thethermostat 52 was continuously calling for cooling. It will munderstood, however, that under normal operation of the air conditioningsystem, the thermostat may not call for cooling until the car attainedsubstantial speed. However, as soon as there is a demand tor cooling andthe thermostat operates to pick up the switch 12, the generator andmotors will be connected in the necessary relation to provide thedesired speed of the motors at the car speed existing when thethermostat is oper ated.

From the foregoing, it is apparent that l have provided a power systemfor railway cars and other vehicles which makw possible the opera tionof alternating current auxiliary devices on the car at speeds withinranges materially less than the range of speeds of the car and,furthermore, that the desired speed of the motors is maintainedregardless of the changes of speed 01 the vehicle.

While I have described my invention in connection with an airconditioning system for railway cars, other applications will readily beapparent to those skilled in the art. I do not, therefore, desire myinvention to be limited to the particular construction shown anddescribed, and I intend in the appended claims to cover allmodifications within the spirit and scope of my invention.

What I claim as new and desire to obtain by Letters Patent of the UnitedStates is:

1. A power system including an alternating current generator, 9.variable speed device arranged to drive said generator, said generatorhaving a plurality of pairs of field poles, an alternating currentmotor, said motor having field exciting windings providing two ranges ofspeed, means for supplying to said motor current produced by saidgenerator to energize said motor, means dependent upon the speed ofsaitL device for changing the effective number of pairs of said fieldpoles to vary the frequency of the current produced by said generatorand for maintainin the range of frequency of the current produced bysaid generator more narrow than the range of speed of said device, anddependent upon the frequency oi the current produced by said generatorfor selecting either oi said ranges of speed 01 said motor.

2. A power system including an alternating current generator, a variablespeed device arranged to drive said generator, said generator having aplurality of pairs of field'poles, means for changing the effectivenumber of pairs of said field poles to provide a range of frequency ofthe current, produced by said generator more narrow than the range ofspeed of said device, an alternating current motor having windingsproviding two ranges of speed, means dependent upon the speed of saiddevice for actuating said pole changing means, and means dependent uponthe frequency of the current produced by said generator for selectingeither of said ranges oi. speed 01' said motor during operation Oif saidgerl erator with either number of efiective pairs oi field poles.

3. A power system including an alternating current generator, a variablespeed device ar= ranged to drive said generator, said generator having aplurality of pairs oi field poles, an alternating current motor, saidmotor having wind.- ings providing two ranges of speed, means forsupplying to said motor current produced by said generator to energizesaid motor, means responsive to the frequency of the current produced bygenerator for changing the effective numleer of pairs of said fieldpoles to vary the frequency the current produced by said generator and.for maintaining the range of frequency or the current produced by saidgenerator more narrow than the range of speed of said device, and meansdependent upon the frequency of the cur rent produced by said generatorfor selecting either of said ranges of speed or said motor.

4. A power system including an alternating current generator, a variablespeed device arranged to drive said generator, said generator having aplurality of pairs of field poles, an alternating current motor, saidmotor having windings providing two ranges of speed, means for supplyingto said motor current produced by said generator to energize said motor,means responsive to the frequency of the current produced by saidgenerator for changing'the effective number of pairs of said field polesto vary the frequency of the current produced by said generator and formaintaining the range of frequency of the current produced by saidgenerator more narrow than the range of speed of said device, meansdependent upon the frequency of the current produced by said generatorfor selecting either of said ranges of speed of said motor, and mean;for connecting to said motor a source of alternating current other thansaid generator and for rendering inoperative said generator polechanging means.

DAVID W. McLENEGAN.

